Patent applications WO-A-90 11092, WO-A-93 19183, WO-A-94 21797, WO-A-95 11307 and WO-A-95 20660 have made use of the recently developed technique of polynucleotide vaccines. It is known that these vaccines use a plasmid capable of expressing, in the cells of the host, a gene inserted into the plasmid and encoding an immunogen. All routes of administration have been proposed (intraperitoneal, intravenous, intramuscular, transcutaneous, intradermal, mucosal, and the like). Various means of vaccination may also be used, such as DNA deposited at the surface of gold particles and discharged so as to penetrate into the cells of the skin of the animal (Tang et al., Nature 356, 152–154, 1992) and liquid jet injectors make it possible to transfect into the skin, muscle, fatty tissues and mammary tissues (Furth et al., Analytical Biochemistry, 205, 365–368, 1992).
These polynucleotide vaccines may be used in the form of naked DNA or in the form of a complex with liposomes or cationic lipids.